Adhesive application without stringing: These 5 points matter

19. December 2022 3 min.

Robert Seiferth, Technical Account Manager and Trainer at Robatech Germany

Do you know the pattern of adhesive beads resulting in stringing? An undesirable pattern that unfortunately happens more often than one would like. Stringing contaminates the product and the production environment. What to do? Sometimes it only takes minor adjustments to achieve a cleaner adhesive application. In this blog post, I'll show you the 5 points that matter.

Adhesive stringing contaminates the production environment

1. THE RIGHT APPLICATION DISTANCE

The distance of the application nozzle to the product has the greatest influence on clean adhesive application. Generally speaking, the closer the nozzle is to the product, the more precise the application pattern will be. As a basic setting, I recommend a distance of 4 mm.

Close-up of jetting head applying adhesive beads

2. THE OPTIMUM TEMPERATURE SETTING

The optimum temperature depends, of course, on the adhesive. Always refer to the adhesive manufacturer’s data sheet! As a general rule: The higher the temperature, the lower the viscosity and elasticity of the hot melt adhesive. And the lower the elasticity of the adhesive, the less stringing during adhesive application.

For gentle heating of the adhesive, proceed as follows: Gradually increase the temperature in the heated hose relative to the melter up to plus 10 °C. The temperature in the melter remains unchanged. Between the heated hose and the application head, also increase the temperature step by step up to plus 5°C. You will notice that the temperature change has a positive effect on the adhesive’s cut-off behavior!

In the following video you can see the difference between adhesive applications with different spray distances and temperature settings.
❌ Distance of nozzle to product with 30 mm too large and temperature with 150 °C too cold
✅ Distance of nozzle to product with 3 mm good and temperature with 175 °C optimal

3. THE RIGHT APPLICATION NOZZLE

The right application nozzle depends on the application. But before you start worrying about whether or not you have the right nozzle, take a good look at your nozzle. Is it intact? Is it clean? Because that is at least as important.
Now to the nozzle shape: It, of course, also has an influence on the occurrence of stringing. Standard application nozzles with ball valves are more prone to stringing, as some adhesive remains in the nozzle tip after closing. Needle valves, on the other hand, eject the adhesive completely when closed. It also depends on whether the nozzle has a drilled channel or a capillary tube. The latter improves adhesive flow so that there is less turbulence and thus less stringing. Last but not least, heat conduction in the nozzle or a nozzle guard against drafts can significantly improve the adhesive’s cut-off behavior.

4. EXTERNAL INFLUENCES

External influences such as drafts from open doors, windows or exhaust systems, fluctuations in the compressed air supply or cooled production halls have a negative effect on the cut-off behavior. Check the compressed air supply in particular; it should be consistently between 5-6 bar.

5. THE RIGHT ADHESIVE

The adhesive must match the application. If all the above adjustments have not brought the desired change, test an adhesive with a lower viscosity. Talk to your adhesive manufacturer or contact your Robatech representative. We will be happy to assist you.

Adhesive application without stringing

What has been your experience? Were these 5 tips helpful? We are looking forward to your feedback in the comments!

Robert Seiferth, Technical Account Manager and Trainer at Robatech Germany

Robert Seiferth is a Technical Account Manager and Trainer at Robatech Germany. For the past 12 years, he has overseen the service hotline, supporting customers from a wide range of industries with technical problems. He passes on his know-how to customers in user training courses.